The present invention relates to fuel injectors for delivery of fuel to the intake system of an internal combustion engine and, more particularly, to an electromagnetic fuel injector having improved wear characteristics.
Many of the components in a modern, internal combustion engine must be manufactured to precise tolerances in order to optimize fuel economy and engine performance and to minimize vehicle emissions. Yet, those same components are expected to operate in the most harsh environments such as at extreme temperatures and under repeated high loads, without premature failure.
It is known in the art to use coatings of various materials on critical components of internal combustion engines for the purpose of improving wear resistance and/or reducing friction. For example, amorphous hydrogenated carbon films and amorphous or nanocrystalline ceramic coatings applied to powertrain components, in particular valve lifters, are described in U.S. Pat. Nos. 5,237,967, 5,249,554, and 5,309,874, the disclosures of which are incorporated herein by reference. Also, U.S. Pat. No. 5,783,261, the disclosure of which is incorporated herein by reference, describes the use of amorphous carbon-based coating containing up to 30% by weight of a carbide-forming material to extend the operating life of a fuel injector valve having a needle operating within a valve body.
In an internal combustion engine, a fuel injector valve mechanism must provide a controlled amount of fuel to each cylinder synchronously with the cycle of the engine in order to control fuel economy, performance and vehicle emissions. The injector surfaces, which are subject to sliding and/or impact contact with other metal surfaces, are typically lubricated by conventional fuel, such as gasoline, thereby preventing undue wear that reduces the useful life of the injector.
With the worldwide fluctuations in the supply of oil, the market has turned to alternate fuels, such as fuels having alcohol components, as a means for supplementing the oil supply. However, the inclusion of an alcohol such as ethanol in a gasoline fuel can greatly increase the fuel""s acidity and reduce its lubricity, resulting in corrosive wear, scuffing, galling, and other damage to both mating parts of sliding and impact surfaces of the fuel injector. The damage can lead to erratic fuel metering by the injector. The magnitude of the effect is dependent on the amount of alcohol added to the fuel and the quality of the alcohol-containing fuel. is Poorer quality ethanol-containing fuels have been found to be contaminated with upwards of 25 ppm sulfuric acid, which greatly exacerbates the above problems and can result in large injector flow shifts (calibration changes) and intermittent valve sticking before the injector reaches even a fraction of its normal life. This, in turn, negatively affects the engine""s ability to precisely control the amount of fuel received in the combustion chamber which can adversely impact fuel economy, performance and emissions.
Reducing the wear of an injector valve assembly, especially one to be used with corrosive ethanol-gasoline mixes or other fuels with lubricity-limiting components, for example, low-sulfur diesel fuels, is thus a highly desirable objective, which is realized by the present invention. Also, what is needed in the art is an injector valve assembly with increased reliability of performance with minimal flow shifts due to wear or valve sticking over its useful life.
The present invention, directed to an electromagnetic fuel injector having improved wear characteristics, comprises a body having a fuel inlet and a fuel outlet. A valve seat is sealably connected to the body, and a moveable valve member positioned at the fuel outlet for controlling the flow of fuel from the outlet. The valve member includes a valve outlet element that provides a sealing interface with the valve seat. The valve member and valve outlet element further comprise wear surfaces that are subject to repeated impact and/or sliding contact. At least a portion of these wear surfaces are coated with a thin layer of diamond-like carbon (DLC) stabilized by inclusion of greater than 30 weight percent of a carbide-forming material selected from the group consisting of silicon, titanium, and tungsten. A solenoid actuator disposed within the body controls the movement of the valve member relative to the valve seat.
It has been found that the quality of the adhesion of the DLC coating can worsen as the coating thickness increases significantly above 6 xcexcm. This can lead to a loss of adhesion, chipping of the coating, and degradation of the coating""s ability to resist metal wear. In another embodiment, a first layer of non-magnetic metal is placed as a foundation below the DLC layer in the area of the magnetic path. The thickness of the non-magnetic layer forms the necessary air gap in the magnetic path thereby permitting a thinner DLC coating to be applied to the region for adhesion optimization.